Mathematical Problems in Engineering

Volume 2018, Article ID 7436054, 11 pages

https://doi.org/10.1155/2018/7436054

## Grey Relational Analysis for Hesitant Fuzzy Sets and Its Applications to Multiattribute Decision-Making

Naval Aviation University, Yantai 264001, China

Correspondence should be addressed to Guidong Sun; moc.361@dgshwds

Received 16 October 2017; Revised 11 March 2018; Accepted 25 March 2018; Published 6 May 2018

Academic Editor: Peide Liu

Copyright © 2018 Xin Guan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

Due to the superiority in expressing the uncertain and vague information, the hesitant fuzzy set (HFS) is regarded as an important tool to deal with multiattribute decision-making (MADM) problems. Quantitative and qualitative fuzzy measures have been proposed to solve such problems from different points. However, most of the existing information measures for HFSs are related to such fuzzy measures as distance, similarity, entropy, and correlation coefficients. The grey relational analysis is omitted. Besides, the existing grey relational analysis for HFSs only considers the range or distance between HFSs data which is only a partial measure of the HFSs. Therefore, in this paper, we improve the grey relational analysis for HFSs and explore a novel slope grey relational degree by considering another factor of HFSs data: the slope. Further, we combine both the distance and slope factors of HFSs data to construct a synthetic grey relational degree that describes the closeness and variation tendency of HFSs simultaneously, greatly enriching the fuzzy measures of HFSs. Furthermore, with the help of the TOPSIS method, we develop the grey relational based MADM methodology to solve the HFSs MADM problems. Finally, combining with two practical MADM examples about energy policy selection and multisensor target recognition, we obtain the most desirable decision results. Compared with the previous methods, the validity, comprehensiveness, and discrimination of the proposed synthetic grey relational degree for HFSs are demonstrated in detail.

#### 1. Introduction

Multiattribute decision-making (MADM) is pervasive and active around human beings’ practical activities. It is an effect and basic method to solve large quantitative and qualitative problems as information fusion, pattern recognition, alternatives selection and evaluation, clustering analysis, military applications, and so forth. However, with the increasing complexity of the decision-making’s environments, the attributes tend to be more and more uncertain. The traditional decision-making methods cannot address these conditions. Therefore, the fuzzy multiattribute decision-making (FMADM) is introduced and widely used to tackle this uncertainty since Zadeh [1] initially proposed the theory of fuzzy set in 1965.

Many researchers have devoted themselves to the FMADM with different types of fuzzy sets, from the traditional fuzzy set to the intuitionistic fuzzy sets (IFSs) and hesitant fuzzy sets (HFSs). IFSs and HFSs are the two most popular fuzzy sets at present, which have been extensively paid attention to. Xu [2] firstly introduced the intuitionistic fuzzy weighted averaging (IFWA) and intuitionistic fuzzy ordered weighted averaging (IFOWA) operators to make the decision. Further, Zhou et al. [3–6] extended these operators by different measures of the IFSs. Recently, Liu et al. [7–15] provided some newest achievements of IFWA and IFOWA operators for IFSs and their extensions by using different kinds of aggregation methods to deal with FMADM, which greatly perfect this theory.

As to the HFS and its extensions, it is a relative new type of fuzzy set which we mainly focus on in this paper. It also attracted great interest from scholars all over the world. Xu and Xia [16, 17], Farhadinia [18, 19], Zeng et al. [20], Zhao et al. [21], Chen et al. [22], and Liao et al. [23] provided a variety of distance, similarity, entropy, and correlation measures for HFSs. Xia et al. [24, 25] and Liao et al. [26, 27] also presented some basic operations and aggregation operators for HFSs. With the help of these basic information measures and aggregation operators, decision can be made with hesitant fuzzy information. He et al. [28] first introduced the expected value and the geometric average value of hesitant multiplicative element (HME) to group decision-making problems. Xu and Zhang [29] developed a novel approach based on TOPSIS and the maximizing deviation method for solving MADM problems with hesitant fuzzy information. Further, Sun et al. [30] constructed an innovative TOPSIS based on synthetic correlation coefficient between HFSs which can handle negative values. Zhang and Xu [31] proposed an interval programming method for solving MAGDM problems with hesitant fuzzy alternatives based on LINMAP. Ashtiani and Azgomi [32] proposed a hesitant FMADM based computational trust model capable of taking into account the fundamental building blocks corresponding to the concept of trust. Ebrahimpour and Eftekhari [33] proposed an innovative method to deal with feature subset selection with HFSs based on maximum relevancy and minimum redundancy approach. Rodríguez et al. [34] introduced the concept of a hesitant fuzzy linguistic term set (HFLTS) to provide a linguistic and computational basis. Liao et al. [35] developed a method to solve the MCDM problem within the context of HFLTSs. Wang et al. [36] developed a likelihood-based TODIM approach for the selection and evaluation with multihesitant fuzzy linguistic information. Meng et al. [37] presented a similarity measure for uncertain linguistic hesitant fuzzy sets and constructed the optimal weight vector for multiattribute decision-making for evaluating corporate environmental performance. Feng et al. [38] proposed a consistency measure method based on the hesitant goal programming model to define the consistency hesitant fuzzy linguistic preference relations. Wu and Xu [39] proposed a large-scale group decision-making consensus model with possibility distribution based hesitant fuzzy preference. Li et al. [40] personalized individual semantics in group decision-making with hesitant fuzzy linguistic terms sets by consensus model. Zhang et al. [41] defined three kinds of additive consistency indices to measure the consistency level of hesitant fuzzy preference relation. Li et al. [42] used the modified TODIM and prospect theory to solve MADM issue of mineral resources evaluation and resources management with hesitant fuzzy linguistic information. Xue and Du [43] defined the multiplicative consistency of hesitant fuzzy preference relations to relax the same number for all elements in HFS and made the decision by fuzzy linear programming method. Liu et al. [44] used the continuous entropy weights and improved Hamacher information aggregation operators to aggregate interval-valued hesitant fuzzy information. Yang et al. [45] used the possibility degree to present a new comparative law for MADM problems with interval-valued hesitant fuzzy soft sets.

Through the above analysis, it is shown that HFSs and their extensions have been effective fuzzy tools for decision-making with uncertainty. However, despite the qualitative and quantitative studies of HFSs, the present work for them mainly focuses on such fuzzy measures as distance, similarity, entropy, and correlation coefficients. The grey relational analysis is omitted. Actually, the traditional grey relational analysis of the fuzzy set takes an important occupation in the fuzzy measure field. It can measure the closeness of two fuzzy sets just like the distance and similarity measures. Many researchers have focused on the grey relational analysis of fuzzy set and proposed several approaches to solve MADM problems. Compared with IFSs, Wei [46, 47], Zhang et al. [48], and Guo [49] had systematically established a series of grey relational analysis (GRA) methods to investigate the MADM problems with intuitionistic fuzzy information. Meanwhile the grey relational analysis for HFSs is limited. Although Li and Wei [50], Sun et al. [51], Wang [52], and Zang et al. [53] have applied GRA for HFSs, DHFSs, and IVDHFSs, the grey relational degrees of them are only a partial measure of the HFSs, which only consider the range or distance between HFSs data. The effects of these grey relational degrees are actually similar to the distance and similarity measures, which limit their applications. Sun et al. [51] considered the slope of the HFSs to form a synthetic grey relational degree, but the combination of this degree is simple and cannot reflect the influence of the whole index space. For these reasons, in this paper, we aim to improve the existing GRA for HFSs and develop a novel grey relational degree that considers both the distance and slope of the HFSs data. The improved grey relational degree satisfies the bidirectional deviation and reflects the influence of the whole index space, which is more reasonable in applications.

Consequently, the motivation of this paper is to explore a novel synthetic grey relational degree for HFSs and develop a methodology based on TOPSIS to solve MADM problems with HFSs information. The novelty of this paper lies in three aspects: (1) exploring the slope grey relational coefficient and slope grey relational degree of the HFSs, (2) constructing the synthetic grey relational coefficient and synthetic grey relational degree of the HFSs by taking into account the distance and slope of the HFSs data, and (3) developing a grey relational based MADM methodology with HFSs information.

The rest of the paper is organized as follows: Section 2 briefly reviews the concepts of HFSs and grey relational analysis theory. In Section 3, we define the grey relational coefficient and grey relational degree for HFSs. We also improve the slope grey relational degree by defining the difference and slope of the HFSs. With the help of the grey relational degree and slope grey relational degree, we construct the synthetic grey relational degree by combining them. In Section 4, we develop a hesitant fuzzy MADM methodology based on the grey relational analysis for HFSs. In Section 5, we apply the proposed grey relational hesitant fuzzy MADM methodology to the practical MADM problems. Finally, the paper ends with some concluding remarks and future challenges in Section 6.

#### 2. Preliminaries

In this section, we recall the HFSs and grey relational analysis theory.

##### 2.1. Hesitant Fuzzy Sets

When an expert makes a decision, he may hesitate to choose the exact membership degree in . For such a circumstance where there are several membership degrees of one element to a set, Torra [54] developed the hesitant fuzzy set (HFS), which is a kind of generalized fuzzy set where the membership degree of an element to a certain set can be illustrated as several different values between 0 and 1. HFS is good at dealing with the situations where people have disagreements or hesitancy when deciding something.

*Definition 1 (see [54]). *Suppose that is a reference set; a hesitant fuzzy set (HFS) on is defined in terms of a function which is when applied to returns a subset of ; that is, where is a set of some different values in , representing the possible membership degrees of the element to the set . For convenience, Xia and Xu [24] call a hesitant fuzzy element (HFE), which is a basic unit of HFS.

##### 2.2. Grey Relational Analysis Theory

Grey relational theory was originally introduced by Deng [55]. The traditional grey relational theory describes the closeness of two variables, which is necessary in the decision-making fields. It has been widely applied to decision-making, pattern recognition, and some other problems under uncertainty, particularly under the discrete data and fuzzy information.

*Definition 2 (see [55]). *For reference set and , the grey relational coefficient is defined bywhere is the identification coefficient, , and generally we let .

The grey relational degree is defined asTake the weight into consideration, let the weight vector of be , , , and the grey relational degree is extended to the weighted grey relational degree:

#### 3. Grey Relational Analysis for HFSs

In this section, we apply grey relational theory to the HFSs and define some novel HFSs expressions based on grey relational theory.

##### 3.1. Grey Relational Definition of HFEs and HFSs

*Definition 3. *For two hesitant fuzzy sets on the fixed set , and , with and , , ; then we define the grey relational coefficient between HFEs and aswhere is the distance between HFEs and , which can be calculated according to following equation: actually, a variety of distance measures for HFEs have been proposed; for more details, please refer to [16–20].

Based on grey relational coefficient between HFEs, the grey relational degree between HFSs and is defined as

In practical applications, the elements in the universe have different weights. Take the weight into consideration and let the weight vector of be , , , and we extend the HFSs grey relational degree to the weighted HFSs grey relational degree as

##### 3.2. Slope Grey Relational Definition for HFEs and HFSs

The HFSs grey relational degree in Section 3.1 mainly focuses on the closeness of the two HFSs; here we improve a novel HFSs grey relational degree called HFSs slope grey relational degree to represent the linear fashion of HFSs. As a departure, we introduce two new concepts of HFEs and HFSs based on Sun et al.’s [51] definition of the difference and slope of the HFSs.

*Definition 4. *For hesitant fuzzy sets with on the fixed set , we define the difference of the HFSs aswhere denotes the difference of the HFEs.where

*Definition 5. *For hesitant fuzzy sets with on the fixed set , the difference of is with ; we define the slope of the HFSs aswhere denotes the slope of the HFEs.where where is the mean of the HFE .The difference and slope of the HFSs can denote the linear fashion of the HFSs clearly, which are useful in practice. With the help of these definitions, we can give the definition of the slope grey relational degree.

*Definition 6. *For two hesitant fuzzy sets on the fixed set , and with and , , ; the differences of them are , , and , , and , , and , ; the slopes of them are with and with ; we define the slope grey relational coefficient between the HFEs and aswhere Based on HFSs slope grey relational coefficient, the HFSs slope grey relational degree is defined asTake the weight into consideration; let the weight vector of be , , , and we extend the HFSs slope grey relational degree to the weighted HFSs slope grey relational degree as

##### 3.3. Synthetic Grey Relational Definition for HFSs

*Definition 7. *For two hesitant fuzzy sets on the fixed set , and with and ; the slopes of them are with and with , , ; then we define the synthetic grey relational coefficient between HFEs and aswhere , which indicates the importance of the closeness and linear fashion of HFSs, respectively, which satisfied and denote the distinguished coefficient of the closeness and linear fashion, and are the distance between HFEs and and the distance between the slopes of HFEs and , respectively, and can be calculated byIf the numbers of values in different HFEs of HFSs are different, we have to extend the shorter one until both of them have the same length when we compare them. We can extend them according to the optimistic or the pessimistic methods in [7, 8].

Based on HFEs synthetic grey relational coefficient, the HFSs synthetic grey relational degree is defined asTake the weight into consideration; let the weight vector of be , , , and we extend the HFSs synthetic grey relational degree to the weighted HFEs synthetic grey relational degree asThe HFSs synthetic grey relational degree takes the considerations of both the closeness and linear fashion of HFSs together, which can better represent the fuzzy measure between the HFSs.

#### 4. The Grey Relational Based MADM Methodology with HFSs Information

In this section, we investigate the grey relational analysis to MADM problems with HFSs information and propose the grey relational based MADM methodology with the help of the TOPSIS method.

Suppose that a hesitant fuzzy MADM problem has alternatives ; each alternative has hesitant fuzzy attribute ; represents the hesitant fuzzy information of the alternatives on the attribute ; is the number of the membership values in ; let be the relative weight vector of the attribute, satisfying the normalization conditions: and . Then all the hesitant fuzzy information can be concisely expressed in matrix format as

Then, according to the TOPSIS approach, we propose the grey relational based MADM methodology with hesitant fuzzy matrix as follows.

*Step 1. *Determine the positive ideal solution (PIS) and negative ideal solution (NIS) of each attribute in the normalized hesitant fuzzy decision matrix to form two new positive and negative HFSs: where and are the new positive and negative HFEs:where and are related to benefit attribute and cost attribute, and are the numbers of the membership values in the new positive and negative HFEs, respectively, and .

*Step 2. *Calculate the HFSs positive and negative grey relational degrees between each alternative and the PIS and NIS, respectively. Here, we can calculate them by the proposed three grey relational degrees: the HFSs grey relational degree, HFSs slope grey relational degree, and HFSs synthetic grey relational degree. where (27) can be obtained according to Definitions 3, 6, and 7.

*Step 3. *Construct the relative closeness to the ideal solution based on the calculated positive and negative grey relational degree. The relative closeness of the alternative with respect to the ideal solution is defined as

*Step 4. *Rank the alternatives according to the decreasing order of their relative closeness. That is, the best alternative is the one with the greatest relative closeness to the ideal solution.

The process of the grey relational based MADM methodology with hesitant fuzzy information is shown in Figure 1.